Organic polysulfides containing two to five or even more sulfur atoms in the molecules have been found useful for many purposes such as additives for elastomers, antioxidants for lubricating oils, intermediates for the production of organic chemicals, insecticides, germicides and as an additive to diesel fuels to improve the octane number and ignition qualities of these fuels. These compounds have also been found useful in the compounding of extreme pressure lubricants and in the acceleration of rubber treating processes.
Such polysulfide compounds can be prepared by reacting mercaptans with elemental sulfur in the presence of a basic catalyst. For example, Biensan et al (U.S. Pat. No. 3,308,166) discloses that polysulfides can be prepared from a mercaptan and sulfur catalyzed by an amine using an alcohol promoter.
It has been shown that an alkyl polysulfide can also be produced by direct addition of sulfur to an alkyl disulfide in the presence of alkali, ammonia, amine, or zinc oxide. For example, sulfur is taken up by a warm, stirred solution of ethyl disulfide containing 1% of triethylamine. See generally E. Reid, Organic Chemistry of Bivalent Sulfur, Vol. III, 1960.
However, it has been discovered that the addition of sulfur to an alkyl disulfide caused substantially incomplete reaction partly due to the low reactivity and solubility of sulfur in alkyl disulfide. Therefore, there is a need to develop an improved process for producing organic polysulfide compounds.